Melbourne - Serena Williams admitted she was frustrated and not at her best as she fought off a stubborn Tamara Zidansek to reach the Australian Open third round on Wednesday.
The American great, one short of Australian Margaret Court's all-time record of 24 Grand Slam titles, faces China's 27th seed Wang Qiang next in Melbourne.
The 38-year-old Williams was never in serious trouble against the 70th-ranked Slovenian Zidansek, winning 6-2, 6-3 at Rod Laver Arena.
But the eighth seed was restrained in her celebrations and said: "It was a good match for me, she was a really good fighter, she did not just let me win."
The 22-year-old Zidansek put up resistance in the second set with Williams twice failing to break when 40-0 up on the Slovenian's serve.
Williams then struggled through her own service game at 3-2 down, with a brief stoppage while the roof closed because of more rain in Melbourne.
Williams finally broke Zidansek's stubborn resolve in the seventh game, getting the break of serve on the way to victory in one hour 18 minutes.
The American great described herself as "frustrated" by her failure to bury her opponent in those two service games.
"I made so many errors in a row and had to battle through my own internal problems," said Williams.
"I knew I had to play better and couldn't keep making unforced errors like that, otherwise it was going to be a long evening for me."
Williams, who has won the Australian Open seven times, thrashed Wang 6-1, 6-0 when they met at the US Open quarter-finals last year.
She dropped just three games in her opening win over Russian teenager Anastasia Potapova on Monday in Melbourne.
Results on day three of the Australian Open Grand Slam at Melbourne Park on Wednesday:
Tennys Sandgren (USA) bt Matteo Berrettini (ITA x8) 7-6 (9/7), 6-4, 4-6, 2-6, 7-5
Sam Querrey (USA) bt Ricardas Berankis (LTU) 7-6 (7/2), 4-6, 6-4, 6-4
Guido Pella (ARG x22) bt Gregoire Barrere (FRA) 6-1, 6-4, 3-6, 6-3
Marton Fucsovics (HUN) bt Jannik Sinner (ITA) 6-4, 6-4, 6-3
Tommy Paul (USA) bt Grigor Dimitrov (BUL x18) 6-4, 7-6 (8/6), 3-6, 6-7 (3/7), 7-6 (10/3)
John Millman (AUS) bt Hubert Hurkacz (POL x31) 6-4, 7-5, 6-3
Stefanos Tsitsipas (GRE x6) bt Philipp Kohlschreiber (GER) walkover
Milos Raonic (CAN x32) bt Cristian Garin (CHI) 6-3, 6-4, 6-2
Marin Cilic (CRO) bt Benoit Paire (FRA x21) 6-2, 6-7 (6/8), 3-6, 6-1, 7-6 (10/3)
Diego Schwartzman (ARG x14) bt Alejandro Davidovich (ESP) 6-1, 6-4, 6-2
Dusan Lajovic (SRB x24) bt Marc Polmans (AUS) 6-2, 6-4, 6-3
Yoshihito Nishioka (JPN) bt Daniel Evans (GBR x30) 6-4, 6-3, 6-4
Novak Djokovic (SRB x2) bt Tatsuma Ito (JPN) 6-1, 6-4, 6-2
Roger Federer (SUI x3) bt Filip Krajinovic (CRO) 6-1, 6-4, 6-1
Fabio Fognini (ITA x12) bt Jordan Thompson (AUS) 7-6 (7/4), 6-1, 3-6, 4-6, 7-6 (10/4)
Roberto Bautista Agut (ESP x9) bt Michael Mmoh (USA) 5-7, 6-2, 6-4, 6-1
Sara Sorribes (ESP) bt Veronika Kudermetova (RUS) 2-6, 6-1, 6-1
Anett Kontaveit (EST x28) bt Astra Sharma (AUS) 6-0, 6-2
Iga Swiatek (POL) bt Timea Babos (HUN) 6-3, 6-2
Carla Suarez (ESP) bt Aryna Sabalenka (BLR x11) 7-6 (8/6), 7-6 (8/6)
Elise Mertens (BEL x16) bt Danka Kovinic (MNE) 6-2, 6-0
Heather Watson (GBR) bt Kristyna Pliskova (CZE) 4-6, 6-3, 6-1
Anastasia Pavlyuchenkova (RUS x30) bt Nina Stojanovic (SRB) 6-1, 7-5
Taylor Townsend (USA) bt Jessica Pegula (USA) 6-4, 7-6 (7/5)
Ashleigh Barty (AUS x1) bt Polona Hercog (SLO) 6-1, 6-4
Elena Rybakina (KAZ x29) bt Greet Minnen (BEL) 6-3, 6-4
Alison Riske (USA x18) bt Lin Zhu (CHN) 6-3, 6-1
Julia Goerges (GER) bt Petra Martic (CRO x13) 4-6, 6-3, 7-5
Maria Sakkari (GRE x22) bt Nao Hibino (JPN) 7-6 (7/4), 6-4
Ekaterina Alexandrova (RUS x25) bt Barbora Krejcikova (CZE) 6-1, 6-3
Petra Kvitova (CZE x7) bt Paula Badosa (ESP) 7-5, 7-5
Naomi Osaka (JPN x3) bt Saisai Zheng (CHN) 6-2, 6-4
Cori Gauff (USA) bt Sorana Cirstea (ROU) 4-6, 6-3, 7-5
Shuai Zhang (CHN) bt Caty McNally (USA) 6-2, 6-4
Sofia Kenin (USA x14) bt Ann Li (USA) 6-1, 6-3
Ons Jabeur (TUN) bt Caroline Garcia (FRA) 1-6, 6-2, 6-3
Caroline Wozniacki (DEN) bt Dayana Yastremska (UKR x23) 7-5, 7-5
Qiang Wang (CHN x27) bt Fiona Ferro (FRA) 6-1, 6-2
Serena Williams (USA x8) bt Tamara Zidansek (SLO) 6-2, 6-3
Madison Keys (USA x10) bt Arantxa Rus (NED) 7-6 (7/3), 6-2